After he returns from the Peninsula Jonathan and is dealing with some tough bouts of PTSD. He turns to medicinal methods, maybe something like laudanum, to help manage troubles such as the hand trembling and not being able to sleep ect. Then he finds he cannot stop. Bring on the hurt dear writer. Have him struggling to hide from Arabella and even Mr. Norrell. Have things get worse before they get better. Even go so far as to have someone catch him and work through getting clean again if you'd like.

I'm open to GEN or romance. People I'm particularly fond of pairing with Strange are: Grant, Arabella, or Norrell. And my knowledge of old timey medicines is fairly limited so if you know other things he might become addicted to at the time speak up!